Most of their surveys involve eg a couple of hours at a focus group and pay £30-50; I can't usually do those but this one was painless!
I signed up for them in the first place from a link on MN I think - they are always looking for more people so here is their site if you want to look. They send out emails now and again if you fit the criteria asking if you use whatever is being looked at - if you don't reply it doesn't matter, they'll still send other invitations.